Protective functions for parallel generators

ABSTRACT

A generator system may include two or more generators electrically connected through a generator bus. A controller receives operation data from a first generator. The operation data may describe a power flow from a second generator to the first generator. From the operation data, either a loss of speed control or a loss of voltage control may be identified at the second generator. The controller may generate a command for the second generator based on the loss of speed control or the loss of voltage control.

This application is a divisional under 35 U.S.C. § 121 and 37 C.F.R.1.53(b) of U.S. patent application Ser. No. 14/459,007 filed on Aug. 13,2014, the disclosure of which is incorporated herein by reference in itsentirety.

TECHNICAL FIELD

This disclosure relates in general to protective functions for parallelgenerators, or more particularly, protective functions for loss ofcontrol of speed or loss of control of excitation in parallelgenerators.

BACKGROUND

Any breaks in power utility service may be unacceptable to somecustomers, and some businesses may have mission critical systems, suchas computer systems in call centers or refrigerators in grocery stores,that rely on constant power. These customers may rely on a backup sourceof power.

One or more generators, or engine-generator sets, may provide backupelectrical energy to the system when the power utility service fails,provide electrical energy in remote areas where no power is available,or provide supplemental electrical energy to the power utility service.Generators also may experience failures. Some failures may be detectedor identified by one or more protective relays. In response to afailure, a protective relay trips a circuit breaker that disconnects thegenerator from the system. However, in some circumstances, a failure inone generator causes a condition in another generator that triggers theprotective relay to disconnect the non-failed generator from the system.Thus, the fully functioning generator is unnecessarily disconnected fromthe system and the system continues to be fed by a malfunctioninggenerator.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary implementations are described herein with reference to thefollowing drawings.

FIG. 1 illustrates an example generator including protectivefunctionality.

FIG. 2 illustrates another example generator including protectivefunctionality.

FIG. 3 illustrates an example system of parallel generators includingprotective functionality.

FIG. 4 illustrates another example system of parallel generatorsincluding protective functionality.

FIG. 5 illustrates another example system of parallel generatorsincluding protective functionality.

FIG. 6 illustrates an example controller for the examples of FIGS. 1-5.

FIG. 7 illustrates an example flowchart for operation of the controllerof FIG. 6.

DETAILED DESCRIPTION

An engine-generator set, which may be referred to as a generator or agenset, may include an engine driven alternator or another combinationof devices for generating electrical energy or power. One or moregenerators may provide power to a load through a generator bus. Thegenerator bus is an electrical conductive path and may be selectivelyconnected through multiple circuit breakers or other types of switchesto the generators, the utility system, and other devices.

Generators may experience various faults and failures. In some systems,any fault or failure results in disconnecting the generator from thebus. Various components may cause the generator to fail, which mayresult in no output or an undesirable output to devices connected to thesystem. However, other faults may be less detrimental. Non-fatal faultsmay include low oil pressure, high coolant temp, low oil level, lowcoolant level, or other examples. Some systems may be designed so thatsuch non-fatal faults result in disconnecting the generator from the busbecause other generators are available as a backup. The system mayinclude n+1 generators, where n is the minimum number of generatorsneeded to support the system. An additional generator is available incase of a failure.

Generator failures may be identified through monitoring the operationand outputs of generators in a system of coupled generators. When thegenerator is not operating properly, it may be removed from the systemby disconnecting the generator from the bus. Some scenarios may causefailures to be incorrectly associated with a properly functioninggenerator. In these scenarios, the failure in one generator causes theoperation or output of the fully operational generator to appear as ifthe fully operational generator is experiencing a failure.

Parallel generators provide power to a common load. The parallelgenerators run at substantially the same speed. Because the generatoroutputs are electrically connected, the outputs of the generator are atthe same voltage. However, power may flow from one generator and toanother generator. The real power is a measurement of the torque on theshafts of the generators. When one shaft has a higher torque than theother shaft, that generator produces more real power than the generatorwith lower torque. If the real power output of a generator is greaterthan the power required by the load, the other generator may absorbpower from that generator. The reactive power is controlled by theexcitation of the field windings of the generators. When one generatorhas higher field excitation, that generator produces more reactive powerthan generator with the lower field excitation. If the reactive poweroutput of a generator is greater than the reactive power required by theload, the other generator may absorb reactive power from that generator.

Any loads connected to the generator bus may absorb power. Inductive orloads may absorb reactive power, and capacitive loads may generatereactive power. There is a net zero real power between the parallelgenerators and the load and a net zero reactive power between thegenerators and the load. That is, any excess real or reactive power thatis not absorbed by the load is absorbed by one or more of thegenerators.

In one example, the malfunction of excitation control in one generatorcauses the failing generator to produce excessive field current. Inanother example, an engine governor malfunction in one generator causesthe failing generator to produce excessive shaft torque. In thesescenarios, which are discussed in more detail below, the malfunctioninggenerator may produce excessive reactive power, measured inkilovolt-amperes reactive (kVAR), or produce excessive real power,measured in kilowatts (kW). The properly functioning generator mayabsorb the excess reactive power or real power in an effort to maintainthe voltage and speed at a target, or both generators may run at thewrong voltage or wrong speed if the properly functioning generator isnot able to absorb enough reactive or real power to maintain voltage andspeed at a target. Either case may cause a protective relay todisconnect the properly functioning generator from the bus.

A generator system may operate in different modes. In an emergency mode,non-fatal faults do not disrupt the operation of the generator. In oneexample, the emergency mode does not allow any faults or failures todisconnect the generator from the bus or shut down the generator. Thegenerator may inform the user (e.g., display a message) when there is afault or failure but continues to run or attempt to run. The generatorcontinues to run until the failures render the generator inoperable(e.g., the crankshaft locks up when the engine oil is burned to lowlevels such that the engine is not adequately lubricated).

Some systems run in emergency mode when there is limited space for asecond generator, such as in marine applications or recreationalvehicles. Other systems may run in emergency mode when a loss of powercould be worse than damaging the generator. For example, in somemilitary applications there is no need to disconnect a generator toprotect it from further damage because more damage is suffered if thesite is without power. Emergency mode operation may be improved whensome types of loss of control failures are identified, allowing failinggenerators in n+1 systems to be disconnected and/or replacementgenerators to be brought online.

FIG. 1 illustrates an example generator 10 including a controller 100,an alternator 15 and an engine 19. The controller 100 may beelectrically coupled directly with the alternator 15 for measuring theoutput of the alternator 15 or the generator bus 11 (e.g., through avoltage sensor or current sensor). The controller 100 may be coupleddirectly with the engine 19 for measuring the speed of the engine 19(e.g., through a tachometer or position sensor). The controller 100 maycontrol the output of the alternator 15 or the speed of the engine 19.The controller 100 may be in communication directly, or indirectlythrough relay 13, with breaker 25 that selectively connects ordisconnects the output of the alternator 15 with the bus 11. Changes inthe speed of the engine are reflected in the frequency of the output ofthe generator. Additional, different, or fewer components may beincluded.

The controller 100 may determine whether any other generators areconnected to the bus 11. In one example, the controller 100 includes aninternal setting through which a user enters the configuration of thegenerator system. In another example, the controller 100 receives datacommunications from other generator controllers in order to identifyconnected generators in the system of parallel generators.

The controller 100 may receive operation data for the generator 10 andother generators connected to the bus 11. The operation data may betransmitted through a dedicated communication line or through the bus11. The operation data may include a connection status for therespective generators and power flows associated with the respectivegenerators.

The controller 100 may determine a loss of speed control or a loss ofvoltage control at the generator 10 based on the operation data for oneor more other generators connected to the bus. In response to the lossof speed control or the loss of voltage control, the controller 100 maygenerate a command for the generator 10. The command may instruct thegenerator 10 to disconnect from the bus 11 (e.g., through controller 100and/or breaker 25).

The determination of a loss of speed control or a loss of voltagecontrol may be based on the power flows of the other generators. Thecontroller 100 may identify reverse power flows from the operation datafor the other generator. A reverse reactive power flow may indicate aloss of voltage control, and a reverse real power flow may indicate aloss of speed control. The reverse reactive power is reactive powerthat, at least in part, flows into generator 10 from the othergenerators. The reverse real power is real power that, at least in part,flows into from generator 10 from other generators. The controller 100may compare the reverse reactive power or a reverse real power to athreshold level indicative of the loss of control. The real power atgenerator 10 may be calculated based on a current measurement and avoltage management. The phase difference between the current measurementand the voltage management of the generator 10 may indicate thedirection of real power (e.g., into generator 10). The real power mayalso be determined using a product of simultaneous samples, among othermethods.

The reactive power at generator 10 may be calculated in a variety oftechniques. A power triangle technique involves the relationship betweenapparent power, active power, and reactive power forming a vectortriangle. Reactive power is equal to the square root of the differencebetween the square of the apparent power and the square of the activepower. A time delay technique may involve a 90 degrees shift (or apredetermined number of digital samples) in either the voltage waveformor the current waveform. The delayed waveform and the other waveform aremultiplied to estimate the reactive power. A filter technique mayprovide a similar delay using a low pass filter. In one embodiment, thereactive power may also be calculated as a function of a frequencychange during the time delay of the 90 degree. For example, the numberof samples of 90 degrees shift may be adjusted according to the totalnumber of samples for a cycle. The direction of the reactive power canbe established by a comparison of the phase angle between the currentwaveform and voltage waveform. The reactive power can be computed for asingle phase or for multiple phases. The reactive power can be computedby connecting a current transformer to a single phase and comparing tothe line-line voltage of another phase, among other methods.

The controller 100 may also receive the results of a comparison ofreactive power or real power from another generator or another generatorcontroller. The results are data indicative of a comparison of agenerator command value for the other generator to a generator outputlevel of the other generator. The controller 100 may generate a breakertrip command for the generator 10 based on the deviation or differenceof the generator command value and generator output level of thegenerator 10 and based on the similar comparison form the othergenerator. For example, the breaker trip command may be generated whenthe deviation for the first generator is more than an allowable rangeand the deviation for the second generator is less than the allowablerange. The threshold level may be a single value. Alternatively, thethreshold level may be part of a threshold curve that is compares thedeviation over time. In one example, the product of the time that thedeviation exceeds the threshold level times the amount that thedeviation exceeds the threshold level is compared to a time cumulativethreshold. In one example, the deviation is integrated over time tocalculate the product. In another example, the threshold level includesa minimum threshold and a maximum threshold. When the deviation exceedsthe minimum threshold, the maximum threshold is adjusted as a functionof time. For example, when the minimum threshold is initially surpassed,the maximum threshold is at a high level. The maximum threshold isadjusted lower over time in steps or continuously to a low level.Therefore, large deviations trip the breaker in short amounts of timeand small deviation trip the breaker if they persist over a longerperiod of time.

The threshold curve may include additional dimensions in which the timeto trip is related to the severity of the loss of control condition. Thesimilar severity-related timing may be for other protective relays on agenerator in order to determine which of the protective relays willoperate in all conditions. Other protective relays include Over Voltage,Over Frequency, Under Voltage, Under Frequency, Over Power, ReversePower, Over Current, Loss of Field (reverse VARs), among others.

FIG. 2 illustrates another example generator 10 in which a regulatorincludes one or both of a voltage regulator 12 a and speed regulator 12b. Similarly, the relay 13 includes one or both of an overvoltage relayand an overfrequency relay. The regulator may experience either a lossof voltage control (the voltage regulator malfunctions) or a loss ofspeed control (the speed regulator malfunctions). A power meteringdevice 18 measures the output (e.g., voltage, current, and/or frequency)from the alternator 14. The output may be sent to the relay 13 andcompared to a threshold value (e.g., voltage threshold, currentthreshold, and/or frequency threshold) by either the power meteringdevice 18 or the relay 13. Additional, different, or fewer componentsmay be included. The relay 13 connects or disconnects the alternator 15from the bus 11 based on the examples described herein.

FIG. 3 illustrates an example system of parallel generators includingprotective functionality. The system includes generators 10 a and 10 bin communication with controllers 200 a and 200 b, respectively, whichmay be internal or external to the generators. A protective relay array13 may include one or more relays for each of the generators to tripbreakers 25 a and 25 b. While it is possible that both of the generators10 a and 10 b experience a failure at the same time, the followingexamples include failures at either generator 10 a or generator 10 b.Additional, different, or fewer components may be included.

The voltage regulator may malfunction for one of the parallelgenerators. For example, the voltage regulator for the generator 10 amay fail to a “full on” failure in which the regulator or controller 200a sends as much field current as possible to the field windings ofgenerator 10 a. The “full on” failure may be caused by a malfunctioningintegrated circuit or a component failure in the voltage regulatorcircuit. For example, in the voltage rectifier circuit, a transistor mayfail into a short circuit condition, a silicon-controller rectifier(SCR) may fail into a diode condition, or a comparator may fail (e.g.,stuck or latched into a specific position). Thus, the output voltage ofgenerator 10 a increases to a level higher than expected. The controllerof generator 10 b detects the higher output voltage of the parallelingbus (caused by generator 10 a) and, in response, generator 10 b attemptsto lower the voltage on the bus 11. Thus, the field current of generator10 b is decreased. Ultimately, generator 10 b may have no field currentand will be absorbing the VARs from generator 10 a.

Even though generator 10 a experienced the failure and generator 10 b isoperating correctly, generator 10 b may absorb reactive power from thebus 11, which may be referred to as reverse VARs or reverse reactivepower. The reverse VARs would cause a conventional protective relay ongenerator 10 b to trip the breaker 25 b. However, controller 200 a mayidentify that generator 10 a is experiencing the failure rather thangenerator 10 b and trip breaker 25 a. Generator controller 200 b mayalso detect that generator 10 a is experiencing the failure and signalgenerator controller 200 a to trip breaker 25 a or generator controller200 b may trip breaker 25 a in the breaker array.

The speed regulator (e.g., engine governor) may malfunction for one ofthe parallel generators. For example, the speed regulator for thegenerator 10 a may fail by sticking to a “full on” failure in which theregulator is instructing the engine of generator 10 a to run as fast aspossible. The engine governor may be electrical or mechanical. Theengine governor may fail to a full-on failure when the fuel meteringrack, throttle plate or an oil seal of a turbocharger fails allowing theengine to use lubricating oil for combustion. Thus, the output ofgenerator 10 a increases to a frequency higher than expected. Thecontroller of generator 10 b detects the higher frequency of generator10 a and, in response, the generator 10 b decreases the quantity of fuelsupplied to the engine in order to regulate the frequency on bus 11. Ifthe load supplied by the generators is low enough, generator 10 b maybecome a load on generator 10 a.

Even though generator 10 a experienced the failure and generator 10 b isoperating correctly, generator 10 b is absorbing power from generator 10a, or experiencing reverse kW condition. A conventional protective relaymay detect the reverse kW and trip the breaker 25 b. However, controller200 b may identify a disruption of the expected speed of the generatorsand determine that the reverse kW at generator 10 b actually indicatesthat generator 10 a has experienced the failure. Thus, controller 200 bdoes not trip breaker 25 b and trips breaker 25 a instead. Thecontroller 200 b may trip breaker 25 a by sending a message tocontroller 200 a. Alternatively, the controller 200 b may directlyinstruct the protective relay array 13 to trip breaker 25 a.

Either or both controllers 200 a and 200 b (“controller 200”) may beconfigured to identify bus voltages and/or output voltages from theoperation data for the generators 10 a and 10 b. The controller 200 maycompare the measured voltage to an expected level. The expected levelmay be a user setting. When the measured voltage deviates from theexpected level at all or by a predetermined allowable range, thecontroller 200 may determine that one of the generators 10 a and 10 b isexperiencing loss of speed control or loss of voltage control.

In order to identify which of the generators 10 a and 10 b is failing,the controller 200 may analyze the power flows. The controller 200 mayidentify reactive power or real power from the operation data for thegenerators 10 a and 10 b. The controller 200 may determine the directionof the power flow and identify the source of power flow as thenon-failing generator and the recipient of the power flows as thefailing generator. The controller 200 may compare the magnitude of thereverse reactive power or the reverse real power to a threshold level.Example threshold levels for the maximum reverse real power may include10%. Example threshold levels for the maximum reverse reactive power mayinclude 15%.

In one example, the threshold level is part of a threshold curve thatprovides different threshold levels for different time durations.Threshold levels may be adjusted higher when the reverse reactive poweror the reverse real power exceed the maximum levels for a short amountof time, and the threshold levels may be adjusted lower when the reversereactive power or the reverse real power exceed the maximum levels for alonger amount of time.

The controller 200 may determine a baseline for reverse power flows. Thecontroller 200 may store reverse power flows during normal operation ofthe generator system. The reverse power flows may be past measurementsof current and voltage at the generator bus 11 used to estimate reactivepower using the power triangle technique, time delay technique, orfilter technique. The baseline may be defined as the average of thereverse power flows or average amplitude of the reverse power flows. Thethreshold level may be based on the baseline for the reverse powerflows.

The controller 200 may control the generator 10 a or generator 10 bbased on the comparison of the reverse power to the threshold level. Inone example, the controller 200 triggers breaker 25 a or breaker 25 b todisconnect one of the generators from the bus 11. When power is beingabsorbed by generator 10 a and the bus speed is lower than expected, thecontroller 200 may trigger breaker 25 a to disconnect generator 10 afrom the bus 11, but when the power is being absorbed by generator 10 aand the bus speed is higher than expected, then the controller 200 maytrigger breaker 25 b to disconnect generator 10 b from the bus 11.

In another example, the controller 200 may control the generator 10 a orgenerator 10 b based on the comparison of the reverse reactive power tothe threshold level. In one example, the controller 200 triggers breaker25 a or breaker 25 b to disconnect one of the generators from the bus11. When reactive power is being absorbed by generator 10 a and the busvoltage is lower than expected, the controller 200 may trigger breaker25 a to disconnect generator 10 a from the bus 11, but when the power isbeing absorbed by generator 10 a and the bus voltage is higher thanexpected, then the controller 200 may trigger breaker 25 b to disconnectgenerator 10 b from the bus 11.

In another example, the controller 200 may bring another generatoronline based on the comparison of the reverse power to the thresholdvalue. When the reactive power for one of the generators exceeds thethreshold value, the controller 200 starts a timer and generates a startcommand for an alternate generator. When the timer reaches apredetermined time (e.g., 10 seconds, 30 seconds, or another value), thecontroller 200 closes to the alternate generator to the bus 11 anddisconnects the failing generator from the generator bus 11.

The threshold level may include multiple levels. The controller 200 maystart the alternate generator and keep the failed generator on the bus11 until the alternate generator is running at a specified level whenthe reverse power is at a first threshold level. However, the controller200 may immediately disconnect the failed generator if the reverse powerreaches a second threshold level.

The controller 200 may operate in multiple modes. The modes may includea normal mode, an emergency mode, and a hybrid mode. In the normal mode,the controller 200 generates a failure signal triggers to trip thebreaker based on a set of faults. In the emergency mode, the controller200 does not generate a failure signal based on any of the set offaults. In the hybrid mode, the controller 200 generates the failuresignal only in reverse power scenarios including reverse real power inone generator indicative of a loss of fuel control in the othergenerator and reverse reactive power in one generator indicative of aloss of excitation control in the other generator. This may avoid damageto equipment that could result from feeding the loads with amalfunctioning generator and may prevent the disconnection of a properlyfunctioning generator from the load, preventing a loss of power to thecritical load while a properly functioning generator is available tosupply power to the critical load.

The mode of the controller 200 may be selected by a user, set by anexternal device, set according to a schedule, or set according tomeasured data. The user may select the mode using a control panel or aswitch. The mode may be selected by a central controller or remotecontroller (e.g., a mobile device in communication with the controller200 through a network). A schedule for the mode may be based on times ofday or days of the week. For example, normal mode may be run on theweekends and emergency mode may be run on weekdays or normal mode may berun during business hours and emergency mode may be run over night. Themode may be set according to measured data. The measured data may beambient conditions (e.g., temperature, humidity, barometric pressure),life of the generator (e.g., engine hours, total lifetime), or a load onthe system.

FIG. 4 illustrates another example system of parallel generatorsincluding protective functionality. A central controller 21 may be incommunication with generators 10 a-b, sensing circuits 16 a-b,regulators 12 a-b and relays 13 a-b. The regulators 12 a-b may includespeed regulators, voltage regulators, or both. The relays 13 a-b areconfigured to switch breakers 25 a-b respectively. The centralcontroller 21 may also be in communication with generators 10 a-b.Additional, different, or fewer components may be included.

The central controller 21 may generate commands for the operation of thegenerators 10 a and 10 b. The commands may instruct the generators tostart running, stop running, increase speeds for the generators,decrease speeds for the generators, increase the field currents, and/ordecrease the field currents. The central controller 21 may receiveoperating parameters of the generators 10 a and 10 b. The operatingparameters may include output voltages, frequencies, currents, reactivepower (e.g., VARs), real power (e.g., kWs), or engine speeds. Theoperating parameters may include measured data collected from one ormore sensors in sensing circuits 16 a-b. The sensors may include anycombination of a voltage sensor, a current sensor, a power sensor, atachometer, a torque sensor, a deflection sensor, a dynamometer, apositional sensor, or a revolution sensor.

The central controller 21 may calculate real power levels and reactivepower levels flowing in and out of the generators 10 a and 10 b based onpower measurements or voltage and current measurements. The centralcontroller 21 may determine voltage levels either at the bus 11 or atthe connection between the bus 11 and the generators 10 a and 10 b. Thecentral controller 21 may determine speed levels based on positionsensors. Table 1 illustrates four example scenarios in the system ofparallel generators.

TABLE 1 Scenario Indicator Failing Generator Working Generator Loss ofBus voltage Reverse reactive Higher than excitation lower than power.expected reactive control (low expected. power output. excitation) Lossof Bus voltage Higher than Reverse reactive excitation higher thanexpected reactive power. control (high expected. power output.excitation) Loss of fuel Speed lower Reverse real Higher than control(low than expected. power. expected real fuel) power output. Loss offuel Speed higher Higher than Reverse real control (high than expectedexpected real power. fuel) power output.

The central controller 21 may initially identify an indicator that oneof the generators has experiences a failure. When the bus voltage orgenerator output voltages deviate from an expected value, the centralcontroller 21 may determine that there is a loss of excitation controlin the generator system. The expected value may be based on a setting ora received generator command sent by the central controller 21. When thevoltage is higher than expected, one of the generators may be producinga high excitation current, and when the voltage is lower than expected,one of the generators may be producing a low excitation current.

When the speed of the generators deviates from an expected value, thecentral controller 21 may determine that there is a loss of fuel controlin the generator system. The expected value may be based on a setting ora received generator command sent by the central controller 21. When thespeed is higher than expected, one of the generators may be experiencinga high throttle/fueling failure, and when the speed is lower thanexpected, one of the generators may be producing a low throttle/fuelingfailure.

The central controller 21 may determine a “full on” or “high level”failure when either the high throttle/fueling failure or the highexcitation current. During a “full on” failure, the central controller21 determines whether one of the generators is experiencing a reversepower flow. If one of the generators is experiencing a reverse powerflow, the other generator is flagged as in error or disconnected fromthe bus.

The central controller 21 may determine a “low level” failure wheneither the high throttle failure or the high excitation current. Duringa “low level” failure, the central controller 21 determines whether oneof the generators is experiencing a reverse power flow. If one of thegenerators is experiencing a reverse power flow, the generatorexperiencing the reverse power flow is flagged as in error ordisconnected from the bus.

More than two generators may be included in the generator system. Whenthree generators are connected to the bus 11, the controller 21 maydetermine which of the three generators is experiencing an odd directionof power flow with respect to the other two. If two of the generatorsare experiencing a reverse power flow, then the other generator isflagged as in error or disconnected from the bus. If one of the threegenerators is experiencing a reverse power flow, then that generator maybe flagged as in error or disconnected from the bus. The same logic canbe applied to four or more generators. If one of the generators isexperiencing a reverse power flow, then either one or two generators ofthe three generators must be malfunctioning. If the bus speed or voltageis low, then the two generators that are not experiencing reverse powerare malfunctioning. If the speed or voltage is high, then the generatorexperiencing the reverse power flow is malfunctioning.

The controller 100, controller 200, or the central controller 21 may beconfigured to perform load shedding. The central controller 21 or thecontroller 100 may generate load shedding commands in response to removeor add portions of the load to the generators 10 a-b. When one of thegenerators is flagged as an error or disconnected from the bus, portionsof the load may be removed so that the load is within the rated outputof the remaining generators. For example, in response to centralcontroller 21 identifying that generator 10 a has experienced a loss ofexcitation control or a low of fuel control based on power flows, thecentral controller 21 may compare the load on the generator system tothe rated output of generator 10 b. If the load exceeds the rated outputof generator 10 b, the central controller 21 may remove a portion of theload from the system.

The generators 10 a-b may also include a fuel supply, a speed governor,a cooling system, an exhaust system, a lubrication system, and astarter. Additional, different, or fewer components may be included.Example types of generators include towable generators, portablegenerators, marine generators, industrial generators, residentialgenerators or other standby generators. The generators may be portableor stationary.

The alternators may include a rotating magnetic field and a stationaryarmature, a rotating armature with a stationary magnetic field, a linearalternator, or a combination of these. The engines may be combustionengines powered by gasoline, diesel fuel, or gaseous fuel. The gaseousfuel may be liquefied petroleum gas (LPG), hydrogen gas, natural gas,biogas, or another gas. The LPG may be or include primarily butane,primarily propane, or a mixture of hydrocarbon gases. The hydrogen gasmay include hydrogen mixed with air or oxygen. The hydrogen gas may bemixed with another fuel when delivered to the engine. Natural gas (e.g.,compressed natural gas (CNG)) may be a hydrocarbon gas mixture. Biogasmay be a gas produced by the breakdown of organic material. The enginesmay also be a turbine turned by steam, water, or wind. Other variationsare possible.

FIG. 5 illustrates another example system of parallel generatorsincluding protective functionality. The system of FIG. 5 may perform anyof the algorithms described herein. Each generator 10 a and 10 b mayinclude a controller 60, an engine 69, an alternator 70, at least onecurrent transformer 68, and a switch 72 (such as a circuit breaker orcontactor). The controller 60 may include logic, software components, orhardware components equivalent to protective relays 61, control logic62, parameter storage 63, paralleling logic 64, a power metering 66 andcommunication interface 65. The engine 69, in addition to the componentsdescribed above, may include an engine control unit 67. The alternator70 may include a voltage regulator 71. Additional, different, or fewercomponents may be included in the system of FIG. 5.

The paralleling logic 64 establishes parallel operation between thegenerator 10 a and the generator 10 b. The paralleling logic determineswhen to open and close the switch 72 in order to bring the generatorsinto parallel operation. The paralleling logic may include speed andvoltage bias outputs that control the speed and voltage for thisgenerator 10 a and engine 69. The communication interface(s) 65communicate to coordinate the paralleling operation.

The parameter storage 62 includes threshold values for the expectedoutput values for the alternator. The threshold values may include anexpected output voltage, an expected output current, and an expectedoutput frequency. The expected values may be defined by control logic 62and/or paralleling logic 64. The expected values may be dependent onuser settings or load characteristics. The parameter storage 62 mayinclude threshold values for power flow between the generators and thebus. The threshold values for power flow may be selected to insure thatpower flows from the generators to the bus. However, the thresholdvalues for power flow may allow for small amounts of reverse power.

The voltage regulator 71 controls output of the alternator 70. The powermetering 66 may monitor measurements of one or more of frequency,voltage or current from the output of the alternator 70. Feedback on theoutput may be measured and provided by the current transformer 68 orother sensor devices. The voltage regulator 71 may experience a failurewhich causes too much field current to be sent (an overcurrentcondition) to the generator 10 a. Similarly, the ECU 67 may fail byincreasing the speed of the engine 69 to an overspeed level. Either theovercurrent condition or the overspeed condition may cause power to betransferred from generator 10 a to generator 10 b.

The control logic 62 may control the speed of the engine 69. The controllogic 62 may identify that the overspeed condition or the overcurrentcondition is occurring in one generator. The control logic 62 maycompare an expected output value (e.g., expected voltage, expectedcurrent, or expected frequency) for the generator 10 a to valuesmeasured by the power metering 66 or receive comparison results from theprotective relay 61.

The control logic 62 may identify that power is being transferred to theother generator. The control logic 62 may receive power measurementsfrom the power metering 66 to identify the magnitude and/or direction ofpower levels being transferred from the generator 10 a to the bus orbeing transferred from the bus to the generator 10 a. The control logic62 may compare expected values for power (e.g., reactive power or realpower) to value measured by power metering 66 receive comparison resultsfrom the protective relay 61.

The control logic 62 may identify a failure at the generator 10 a whenthe measured value exceeds the expected output value and power isflowing from generator 10 a to generator 10 b. In response to thefailure, the control logic 62 may generate a command for the switch 72to disconnect the generator 10 a from the bus. The communicationinterface(s) 65 communicate to exchange measured values and comparisonresults between the generators.

FIG. 6 illustrates an example generator controller 100 of the system forprotective functions. The controller 100 may include a processor 300, amemory 302, and a communication interface 303. The controller 100 may beconnected to a workstation 309 or another external device (e.g., controlpanel) and/or a database 307. Optionally, the generator controller 100may include an input device 305 and/or a sensing circuit 311. Thesensing circuit 311 receives sensor measurements (e.g., power, current,voltage, speed) for the operation of the generator or connectedgenerators. Additional, different, or fewer components may be included.

The memory 302 may be configured to store expected operating parametersfor a system of generators. The expected operating parameters may bebased on settings sent to the system of generators or rated outputlevels for the system of generators. The expected operating parametersmay include a threshold for reverse power and a threshold for outputvoltage. The input device 305 may receive user inputs for sending thepower threshold, speed thresholds, and voltage thresholds.

The communication interface 303 or processor 300 may receive operationdata of current output levels for the system of generators. Theoperation data may include real power levels, reactive power levels andan output voltage level for each generator in the system of generators.The processor 300 may determine deviations between a reverse power levelfor the first generator and the threshold for reverse power. Theprocessor 300 may also determine deviations between an output voltageand the threshold for output voltage and/or speed and threshold forspeed.

The processor 300 may control one or more of the system of generators inresponse to the reverse power level exceeding the threshold. In oneexample, the processor 300 generates a disconnection command for thegenerator receiving the reverse power when the output voltage is lowerthan the expected level or the speed is lower than the expected level.In another example, the processor 300 generates a disconnection commandfor the generator not receiving the reverse power when the outputvoltage is higher than the expected level or the speed is higher thanthe expected level.

FIG. 7 illustrates example flowchart for operation of the controller ofFIG. 5. The methods in FIG. 7 may, in some instances, be implemented aslogic or software executable by a controller, such as controller 100 orcontroller 200. Additional, different, or fewer acts may be provided.The acts may be performed in the order shown or other orders. The actsmay also be repeated.

At act S101, the controller 100 measures reverse real power in a powerflow between two or more generators (e.g., from generator A to generatorB). At act S103, the controller 100 measured reverse reactive power inthe power flow. When power is transferred from one generator to anothergenerator, there is a failure in the system. Using any of the techniquesabove, the controller 100 identifies the power flow as either real orreactive.

At act S105, when the power flow is real, the controller 100 determineswhether the speed of one or more of the generators is higher or lowerthan the predicted speed. When the speed is high, then the generatorthat is the source of the excess power is failing. Therefore, at actS113, generator A is identifies as failing. When the speed is low, thegenerator that is the sink of the excess power is failing. Therefore, atS109, generator B is identified as failing.

At act S107, when the power flow is reactive, the controller 100determines whether the output voltage of the generator system is higheror lower that the predicted voltage. When the voltage is high, then thegenerator that is the source of the excess power is failing. Therefore,at act S113, generator A is identified as failing. When the voltage islow, the generator that is the sink of the excess power is failing.Therefore, at S109, generator B is identified as failing.

At act S111, when generator B is failing, generator B may bedisconnected from the generator system by triggering a circuit breakerassociated with generator B. At act S115, when generator A is failing,generator A may be disconnected from the generator system by triggeringa circuit breaker associated with generator A.

Other actions may be taken. In one example, controller 100 connects areplacement regulator (e.g., speed governor or voltage regulator) in thefailing generator. In other words, using switches, the controller 100removes the regulator and connects a new regulator. The controller 100may generate an error message for the user that the regulator or thegenerator has failed and should be repaired or replaced. The errormessage may describe whether the generator has experienced a loss offuel control or a loss of excitation control.

The processor 300 may include a general processor, digital signalprocessor, an application specific integrated circuit (ASIC), fieldprogrammable gate array (FPGA), analog circuit, digital circuit,combinations thereof, or other now known or later developed processor.The processor 300 may be a single device or combinations of devices,such as associated with a network, distributed processing, or cloudcomputing.

The memory 302 may be a volatile memory or a non-volatile memory. Thememory 302 may include one or more of a read only memory (ROM), randomaccess memory (RAM), a flash memory, an electronic erasable program readonly memory (EEPROM), or other type of memory. The memory 302 may beremovable from the network device, such as a secure digital (SD) memorycard.

The input device 305 may include a control panel coupled to orintegrated with one of the generators. The input device 305 may be oneor more buttons, keypad, keyboard, mouse, touch pad, voice recognitioncircuit, or other device or component for inputting data to thecontroller 100. The input device 203 and a display may be combined as atouch screen. The input device 203 may be an interface connected to amobile device such as a smart phone, computer, or tablet for sendinguser settings to the controller 100.

In addition to ingress ports and egress ports, the communicationinterface 303 may include any operable connection. An operableconnection may be one in which signals, physical communications, and/orlogical communications may be sent and/or received. An operableconnection may include a physical interface, an electrical interface,and/or a data interface.

The communication interface 303 may be connected to a network. Thenetwork may include wired networks (e.g., Ethernet), wireless networks,or combinations thereof. The wireless network may be a cellulartelephone network, an 802.11, 802.16, 802.20, or WiMax network. Further,the network may be a public network, such as the Internet, a privatenetwork, such as an intranet, or combinations thereof, and may utilize avariety of networking protocols now available or later developedincluding, but not limited to TCP/IP based networking protocols.

While the computer-readable medium (e.g., memory 302 or database 307) isshown to be a single medium, the term “computer-readable medium”includes a single medium or multiple media, such as a centralized ordistributed database, and/or associated caches and servers that storeone or more sets of instructions. The term “computer-readable medium”shall also include any medium that is capable of storing, encoding orcarrying a set of instructions for execution by a processor or thatcause a computer system to perform any one or more of the methods oroperations disclosed herein.

In a particular non-limiting, exemplary embodiment, thecomputer-readable medium can include a solid-state memory such as amemory card or other package that houses one or more non-volatileread-only memories. Further, the computer-readable medium can be arandom access memory or other volatile re-writable memory. Additionally,the computer-readable medium can include a magneto-optical or opticalmedium, such as a disk or tapes or other storage device to capturecarrier wave signals such as a signal communicated over a transmissionmedium. A digital file attachment to an e-mail or other self-containedinformation archive or set of archives may be considered a distributionmedium that is a tangible storage medium. Accordingly, the disclosure isconsidered to include any one or more of a computer-readable medium or adistribution medium and other equivalents and successor media, in whichdata or instructions may be stored. The computer-readable medium may benon-transitory, which includes all tangible computer-readable media.

In an alternative embodiment, dedicated hardware implementations, suchas application specific integrated circuits, programmable logic arraysand other hardware devices, can be constructed to implement one or moreof the methods described herein. Applications that may include theapparatus and systems of various embodiments can broadly include avariety of electronic and computer systems. One or more embodimentsdescribed herein may implement functions using two or more specificinterconnected hardware modules or devices with related control and datasignals that can be communicated between and through the modules, or asportions of an application-specific integrated circuit. Accordingly, thepresent system encompasses software, firmware, and hardwareimplementations.

In accordance with various embodiments of the present disclosure, themethods described herein may be implemented by software programsexecutable by a computer system. Further, in an exemplary, non-limitedembodiment, implementations can include distributed processing,component/object distributed processing, and parallel processing.Alternatively, virtual computer system processing can be constructed toimplement one or more of the methods or functionality as describedherein.

As used in this application, the term ‘circuitry’ or ‘circuit’ refers toall of the following: (a) hardware-only circuit implementations (such asimplementations in only analog and/or digital circuitry) and (b) tocombinations of circuits and software (and/or firmware), such as (asapplicable): (i) to a combination of processor(s) or (ii) to portions ofprocessor(s)/software (including digital signal processor(s)), software,and memory(ies) that work together to cause an apparatus, such as amobile phone or server, to perform various functions) and (c) tocircuits, such as a microprocessor(s) or a portion of amicroprocessor(s), that require software or firmware for operation, evenif the software or firmware is not physically present.

This definition of ‘circuitry’ applies to all uses of this term in thisapplication, including in any claims. As a further example, as used inthis application, the term “circuitry” would also cover animplementation of merely a processor (or multiple processors) or portionof a processor and its (or their) accompanying software and/or firmware.The term “circuitry” would also cover, for example and if applicable tothe particular claim element, a baseband integrated circuit orapplications processor integrated circuit for a mobile phone or asimilar integrated circuit in server, a cellular network device, orother network device.

Processors suitable for the execution of a computer program include, byway of example, both general and special purpose microprocessors, andanyone or more processors of any kind of digital computer. Generally, aprocessor may receive instructions and data from a read only memory or arandom access memory or both. The essential elements of a computer are aprocessor for performing instructions and one or more memory devices forstoring instructions and data. Generally, a computer may also include,or be operatively coupled to receive data from or transfer data to, orboth, one or more mass storage devices for storing data, e.g., magnetic,magneto optical disks, or optical disks. Computer readable mediasuitable for storing computer program instructions and data include allforms of non-volatile memory, media and memory devices, including by wayof example semiconductor memory devices, e.g., EPROM, EEPROM, and flashmemory devices; magnetic disks, e.g., internal hard disks or removabledisks; magneto optical disks; and CD ROM and DVD-ROM disks. Theprocessor and the memory can be supplemented by, or incorporated in,special purpose logic circuitry.

The illustrations of the embodiments described herein are intended toprovide a general understanding of the structure of the variousembodiments. The illustrations are not intended to serve as a completedescription of all of the elements and features of apparatus and systemsthat utilize the structures or methods described herein. Many otherembodiments may be apparent to those of skill in the art upon reviewingthe disclosure. Other embodiments may be utilized and derived from thedisclosure, such that structural and logical substitutions and changesmay be made without departing from the scope of the disclosure.Additionally, the illustrations are merely representational and may notbe drawn to scale. Certain proportions within the illustrations may beexaggerated, while other proportions may be minimized. Accordingly, thedisclosure and the figures are to be regarded as illustrative ratherthan restrictive.

While this specification contains many specifics, these should not beconstrued as limitations on the scope of the invention or of what may beclaimed, but rather as descriptions of features specific to particularembodiments of the invention. Certain features that are described inthis specification in the context of separate embodiments can also beimplemented in combination in a single embodiment. Conversely, variousfeatures that are described in the context of a single embodiment canalso be implemented in multiple embodiments separately or in anysuitable sub-combination. Moreover, although features may be describedabove as acting in certain combinations and even initially claimed assuch, one or more features from a claimed combination can in some casesbe excised from the combination, and the claimed combination may bedirected to a sub-combination or variation of a sub-combination.

One or more embodiments of the disclosure may be referred to herein,individually and/or collectively, by the term “invention” merely forconvenience and without intending to voluntarily limit the scope of thisapplication to any particular invention or inventive concept. Moreover,although specific embodiments have been illustrated and describedherein, it should be appreciated that any subsequent arrangementdesigned to achieve the same or similar purpose may be substituted forthe specific embodiments shown. This disclosure is intended to cover anyand all subsequent adaptations or variations of various embodiments.Combinations of the above embodiments, and other embodiments notspecifically described herein, will be apparent to those of skill in theart upon reviewing the description.

It is intended that the foregoing detailed description be regarded asillustrative rather than limiting and that it is understood that thefollowing claims including all equivalents are intended to define thescope of the invention. The claims should not be read as limited to thedescribed order or elements unless stated to that effect. Therefore, allembodiments that come within the scope and spirit of the followingclaims and equivalents thereto are claimed as the invention.

We claim:
 1. An apparatus comprising: a memory configured to storeexpected operating parameters for a system of generators including afirst generator and a second generator, wherein the expected operatingparameters include a threshold for reverse power and a threshold foroutput voltage; and a processor configured to receive operation data forthe first generator and the second generator, wherein the operation datainclude reverse power levels and an output voltage level, wherein theprocessor is configured to determine deviations between a reverse powerlevel for the first generator and the threshold for reverse power andbetween an output voltage and the threshold for output voltage, whereinthe processor is configured to generate a disconnection command for thesecond generator when the deviation for the reverse power level for thefirst generator exceeds an allowable range.
 2. The apparatus of claim 1,wherein the allowable range is a first allowable range, wherein theprocessor is configured to generate a disconnection command for thesecond generator when the deviation for the reverse power level for thefirst generator exceeds the first allowable range and the deviationbetween the output voltage and the threshold for output voltage exceedsa second allowable range.
 3. The apparatus of claim 1, wherein thedeviation for the reverse power level for the first generator indicatesreverse real power and a loss of speed control at the second generator.4. The apparatus of claim 1, wherein the deviation for the reverse powerlevel for the first generator indicates reverse reactive power and aloss of excitation control at the second generator.
 5. The apparatus ofclaim 1, wherein the processor is operable in a normal mode and anemergency mode, wherein, in the normal mode, a disconnection command forthe second generator is initiated when the deviation for the reversepower level for the first generator exceeds the allowable range, andwherein, in the normal mode, no disconnection command is initiated. 6.The apparatus of claim 5, wherein the processor is operable in a hybridmode for initiating a timer based on the deviation for the reverse powerlevel for the first generator exceeds the allowable range, wherein thedisconnection command is initiated when the timer reaches apredetermined level.
 7. A system comprising: a first generator coupledto a generator bus; a second generator coupled to the generator bus; anda controller configured to identify a power flow from the firstgenerator to the second generator through the generator bus anddetermine a loss of generator control based on operation data for thefirst generator or the second generator, wherein the controllerdisconnects the second generator based on a loss of speed control or aloss of voltage control, wherein the power flow includes reactive powerwhen the loss of generator control is a loss of excitation control andthe power flow includes real power when the loss of generator control isa loss of speed control.
 8. A method comprising: storing, at a memory,expected operating parameters for a system of generators including afirst generator and a second generator, wherein the expected operatingparameters include a threshold for reverse power and a threshold foroutput voltage; receiving, at a processor, operation data for the firstgenerator and the second generator, wherein the operation data includereverse power levels and an output voltage level, determining, by theprocessor, deviations between a reverse power level for the firstgenerator and the threshold for reverse power; determining, by theprocessor, deviations between an output voltage and the threshold foroutput voltage; and initiating, in a normal mode, a disconnectioncommand for the second generator is initiated when the deviation for thereverse power level for the first generator exceeds an allowable range,and wherein, in the normal mode, no disconnection command is initiated.9. The method of claim 8, further comprising: generating a disconnectioncommand for the second generator when the deviation for the reversepower level for the first generator exceeds a first allowable range andthe deviation between the output voltage and the threshold for outputvoltage exceeds a second allowable range.
 10. The method of claim 8,further comprising: generating a disconnection command for the secondgenerator when the deviation for the reverse power level for the firstgenerator exceeds an allowable range.
 11. The method of claim 10,wherein the deviation for the reverse power level for the firstgenerator indicates reverse real power and a loss of speed control atthe second generator.
 12. The method of claim 10, wherein the deviationfor the reverse power level for the first generator indicates reversereactive power and a loss of excitation control at the second generator.13. The method of claim 8, further comprising: initiating, in a hybridmode, a timer based on the deviation for the reverse power level for thefirst generator exceeds the allowable range, wherein the disconnectioncommand is initiated when the timer reaches a predetermined level. 14.The method of claim 8, further comprising: receiving a user selectionfor an operation mode selected from a normal mode, a hybrid mode, and anemergency mode.
 15. The method of claim 14, wherein the emergency modemaintains connections during failures.
 16. The method of claim 14,further comprising: accessing, from the memory, an operation mode from aplurality of operation modes based on handling failures in the system ofgenerators.